STP433

Hearing

Sound is the perception by humans of vibrations in some physical medium, usually air. These physical vibrations of the air are evidenced by alternating rarefractions and compressions. Man's primary sense organ for the sound stimulus is the ear (Fig. 1). The external ear consists of the pinna or auricle. From this a canal, the auditory meatus, leads into the skull. This canal terminates at the eardrum, or tympanic membrane. A small muscle, the tensor tympani, regulates the tension of the tympanic membrane.